1. Field of the Invention
This invention relates to a disposable syringe, more particularly to a disposable syringe which enables a needle unit to be retracted within a barrel after use for safe disposal and use.
2. Description of the Related Art
Referring to FIG. 1, a conventional disposable syringe assembly 10 is shown to include a barrel 11, a plunger 12 and a needle unit 13. The barrel 11 has an open neck end portion 111 to which a needle hub 131 of the needle unit 13 is attached, and an open rear end from which the plunger 12 is slidably inserted into the barrel 11. A forward end 121 of the plunger 12 is snugly fitted against, but is nevertheless slidable along, the inner surface of the barrel 11 through a distance (L). The needle unit 13 further has a needle 132 extending from the needle hub 131, and a cap 133 with an open end which is fitted around an outer edge of the needle hub 131, with the needle 132 enclosed within the cap 133. The cap 133 is removed from the needle hub 131 when the syringe assembly 10 is to be used, and is sleeved back after use to ensure that the needle 132 is covered. Thereafter, the needle unit 13 is detached from the barrel 11 along with the cap 133 covering the needle 132.
However, the medical or nursing personnel who has to handle the conventional disposable syringe assembly 10 is exposed to the risk of being pricked by the needle 132 when sleeving the cap 133 back on the needle hub 131 after using the disposable syringe assembly 10 since the dimension of the open end of the cap 133 is small. Moreover, as forward movement of the forward end 121 of the plunger 12 terminates at the point (P1), some medicine or blood may remain within the neck end portion 111, which may cause contamination to the personnel who is unfortunately pricked by the needle 132.